The proposed research is concerned with the ontogeny of ingestive behavior, especially suckling in albino rats. Three specific aims are proposed. 1) Included in the first aim are experiments to identify the critical substance in pup saliva that elicits nipple attachment during the nursing-suckling period. We have already identified dimethyl disulfide as such a substance in the saliva of five day old pups. We also propose to identify the prenatal and immediate postnatal events that are sufficient to bias the infant's very first nipple attachment. Our preliminary results strongly implicate a prenatal factor. Finally, we will identify postnatal events that are sufficient to transfer the ability to elicit nipple attachment from one stimulus to another. The second aim will identify internal controls over milk-intake at the nipple. Included in this aim is an analysis of the recent finding that insulin increases milk-intake via suckling but not feeding. The third aim is to initiate a functional analysis of the developing rat nervous system through the method on intracranial self-stimulation. We have already developed the techniques for this study and have demonstrated that three day old rats learn a response that produces electrical stimulation to the medial forebrain bundle. We will extend this analysis to other brain sites and will attempt to influence self-stimulation rate by manipulating the developing norepinephrine and dopamine systems.